Rotating belt wafer edge cleaning apparatus

ABSTRACT

An apparatus for cleaning edges and/or bevel areas of substrates. In one embodiment, the present invention provides a cleaning mechanism that cleans particles off the edge of the wafer based upon friction at the contact point between the wafer and a rotating belt.

This is a Divisional Application of Ser. No. 09/128,343 filed on Aug. 3,1998 U.S. Pat. No. 6,357,071, which is a Divisional Application of Ser.No. 08/777,518 filed on Dec. 30, 1996 U.S. Pat. No. 5,868,857.

FIELD OF THE INVENTION

The present invention relates to the field of semiconductor waferprocessing; more particularly, the present invention relates to cleaningthe edges and/or bevel areas of semiconductor wafers.

BACKGROUND OF THE INVENTION

Semiconductor manufacturers use semiconductor wafers as the base formanufacturing integrated circuits. In one step of the manufacturingprocess, the wafers are put through chemical mechanical polishing (CMP).CMP is becoming the main planarization technology for both dielectricand metal layers. For the CMP of dielectric layers, such as BPSG,BPTEOS, and PECVD Oxides (often referred to as the ILD0, ILD1, ILD2 . .. layers, respectively), a fumed silica-based slurry is normally used.Other slurries, such as dispersed silica, fumed or dispersed allumina,are also being used for CMP of both oxides and metals (such as tungsten(W), copper (Cu), aluminum (al), and titanium (Ti)). When the CMPprocess is completed, the wafers' surfaces are covered in particles,referred to as a slurry residue. At later steps in the process flow,some of this slurry residue is redistributed across the front of thewafer, thereby resulting in a loss in die yield and/or deviceperformance. To prevent the slurry redistribution, all surfaces of awafer must be free of contamination.

Different post CMP cleaning methods have been introduced in the last fewyears. These include cleaning the wafers in wet stations usingconventional wet cleaning methods, such as SC1, HF and megasoniccleaning. other cleaning methods in use are based or scrubbing waferswith brushes of various kinds and configurations using DI water or acombination of DI with chemicals such as Ammonia and Citric acid.

One system used to remove wafer contaminants is a double sided scrubber.In a double sided scrubber, a semiconductor wafer is scrubbedsimultaneously on both sides by brushes. Since the wafer is beingscrubbed simultaneously on both sides by the brushes, there must be away of holding the wafer in place and rotating the wafer so the entiresurface of the wafer is cleaned. A mechanism used for this purpose iscommonly referred to as a roller.

Today, double sided scrubbers are usually automated and comprise aconveyor type mechanism, rollers, and brushes. In general, the waferlies flat on the conveyor mechanism and the conveyor mechanism moves thewafer into the brushes. While being scrubbed, the wafer is supported (orheld horizontally) by the conveyor mechanism, brushes, rollers, or acombination thereof. FIG. 1 illustrates a conventional double sidedwafer scrubber. Referring to FIG. 1, a wafer 102 is being scrubbed bybrushes, one of which is shown as brush 110 and the other being beneathwafer 102 and directly below brush 110. Rollers 108 rotate wafer 102 sothe entire wafer surface may be cleaned. Each of brushes 110 is rotatedabout its central axis by a motor 106. The rotary motion of rollers 108is then transferred to wafer 102 when the edge of each of rollers 109comes into contact with the outer edge of wafer 102.

Although conventional brush cleaning systems can effectively clean thefront and backs of semiconductor substrates, such systems fail toprovide a sufficient amount of mechanical energy at the edge/bevel toremove contamination.

The present invention provides an apparatus that cleans the edge ofsubstrates, including the bevel area when present.

SUMMARY OF THE INVENTION

An apparatus for cleaning edges and/or bevel areas of substrates isdescribed. In one embodiment, the present invention provides a cleaningmechanism that cleans particles off the edge of the wafer based uponfriction at the contact point between the wafer and a rotating belt.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the invention, which, however, should not be taken tolimit the invention to the specific embodiments, but are for explanationand understanding only.

FIG. 1 illustrates a prior art double sided wafer scrubber.

FIG. 2A illustrates a side view of a rotating belt edge cleaningapparatus in one embodiment of the present invention with the rotatingbelt rotated away from the edge of a wafer.

FIG. 2B illustrates a side view of the rotating belt edge cleaningapparatus of FIG. 2A with the rotating belt engaged against the edge ofthe wafer.

FIG. 3A illustrates a rotating belt edge cleaning apparatus attached toa carrier that moves to engage or disengage the rotating belt from theedge of a wafer.

FIG. 3B illustrates another embodiment of the present invention.

FIG. 4A illustrates a side view of a rotating belt edge cleaningapparatus in another embodiment of the present invention with therotating belt rotated away from the edge of a wafer.

FIG. 4B illustrates a side view of the rotating belt edge cleaningmechanism of FIG. 4A showing the rotational movement of the mechanism asit engages the edge of the wafer.

FIG. 5A illustrates a perspective view of a double-sided edge scrubbersystem that includes a rotating belt edge cleaning apparatus.

FIG. 5B illustrates a perspective view of the double-sided scrubber ofFIG. 5A having a jet spray nozzle for delivering a cleaning fluid to thesurface of the wafer.

FIG. 6 illustrates a perspective view of a double-sided edge scrubbersystem having a plurality of rotating belt edge cleaning apparatus.

DETAILED DESCRIPTION

An apparatus for cleaning edges of contaminated substrates is described.The cleaning process may be used in double sided scrubber systems orother systems, such as, for instance, chemical mechanical polishingsystems or flat panel display manufacturing systems. In the followingdescription, numerous specific details are set forth such as rotationspeeds, chemicals, pressures, etc., in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knowncomponents, structures and techniques have not been shown in detail inorder to avoid obscuring the present invention.

The present invention provides a method and apparatus that cleans theedge of substrates, including the bevel area when present. In thepresent invention, particles are removed from the edge and/or bevel area(or any other surface sloping from the edge to the top or bottom of thesubstrate) using an edge scrubbing mechanism that may be incorporatedinto a scrubber tool.

Although the present invention is described in conjunction with thescrubbing of a wafer, it will be appreciated that any similarly shaped,i.e. generally flat, substrate, may be processed by the methods andapparatuses of the present invention. Further, it will be appreciatedthat reference to a wafer or substrate may include a bare or puresemiconductor substrate, with or without doping, a semiconductorsubstrate with epitaxial layers, a semiconductor substrate incorporatingone or more device layers at any stage of processing, other types ofsubstrates incorporating one or more semiconductor layers such assubstrates having semiconductor on insulator (SOI) devices, two ormultiple substrates bonded to each other, or substrates for processingother apparatuses and devices such as flat panel displays, multichipmodules, etc.

FIGS. 2A and 2B illustrate a wafer edge cleaning device in oneembodiment of the present invention. As shown, the edge 203 of arotating wafer 202 is cleaned by positioning a rotating belt 206adjacent to the wafer edge 203 such that an abrasive outer surface 208of the belt slides across the edge surface. The frictional forcesgenerated between the outer surface 208 of belt 206 and edge 203 resultin the removal of contaminates residing at the contact points at thebelt/edge interface. The relative velocity difference between belt 206and wafer 202 also contributes to the removal of particles from the edgesurface. The inner surface 209 of belt 206 is acted upon by the outersurfaces 214 and 216 of rollers 210 and 212, respectively. Each ofrollers 210 and 212 have an axis of rotation 218 and 220, respectively.The location of axis 218 is fixed, whereas axis 220 is permitted to movealong a path 222 as roller 220 is pivoted in an upward direction aboutfixed axis 218. A motor (not shown) is coupled to roller 210 to providerotational movement to the roller. The resistance between the outersurface 214 of roller 210 and inner surface 209 of belt imparts therotational movement of roller 210 to belt 206.

As shown in FIGS. 2A and 2B, the edge 203 of wafer 202 is cleaned byplacing the wafer adjacent edge cleaning apparatus 200 and pivotingroller 220 in an upward direction about axis 218 so that the outersurface 208 of belt 206 contacts the edge 203 of wafer 202. In oneembodiment, belt 206 comprises an elastomer material that is stretchedto fit over rollers 210 and 212. Alternatively, roller 220 may beslidably mounted. In such an embodiment, belt 206 is placed around theouter surfaces of the rollers and the tension of belt 206 is adjusted byslidably adjusting the position of roller 220. The outer surface 208 ofbelt 206 is textured such that sufficient frictional forces are producedat the belt/wafer edge interface to remove contaminates from the waferedge during cleaning. The surface roughness of surface 208 is selectedto facilitate the removal of unwanted particles from the wafer's edgewithout damaging the wafer itself. In some instances, the texture ofbelt 206 may vary along the circumference of the belt. In this manner,one portion of the belt may be used for removing one type of contaminatewhile another portion of the belt may be used to remove another type ofcontaminate.

FIG. 3A illustrates another method of cleaning the edge of a wafer. Asshown in FIG. 3A, rollers 210 and 212 are attached to support structure300 at axis 218 and 220. In lieu of using a pivoting action to bring thebelt 206 into contact with wafer edge 203, the lateral movement ofsupport structure 300 is used to position the edge cleaning apparatus.In addition, rollers 210 and 212 may be spring mounted to structure 300by springs 310 and 312. By spring mounting rollers 210 and 212 tostructure 300, the amount of force exerted upon edge 203 by belt 206 ismore accurately controlled.

In one embodiment, the width of belt 206 is approximately 0.5 inches.The outer surface 208 of belt 206 may comprise PVA, nylon, orpolyurethane.

With reference to FIGS. 4A and 4B, a belt-type edge cleaning apparatus400 in another embodiment of the present invention is shown. Thebelt-type edge cleaning apparatus 400 is similar to the edge cleaningapparatus 200 of FIGS. 2A and 2B, however, apparatus 400 includes threerollers instead of two. Edge cleaning apparatus 400 includes a belt 406having an inner surface 409 and an outer surface 408. Belt 406 is heldin position and rotated by three rollers 410-412. Each of rollers410-412 has an axis of rotation 416, 417 and 418, respectively. Axis 416is stationary, whereas axes 417 and 418 are permitted to move generallyin the direction indicated in FIG. 4B as the belt assembly is pivotedupward about axis 416. A motor (not shown) is coupled to roller 410 toprovide rotational movement to belt 406. As shown in FIG. 4B, the edge403 of wafer 402 is cleaned by placing the edge of wafer 402 inproximity to rotating belt edge cleaning apparatus 400 and pivotingapparatus 400 upward about stationary axis 416 to engage the outersurface 408 of belt 406 against wafer edge 403.

Turning now to FIG. 5A, edge cleaning apparatus 500 is shownincorporated into a double sided scrubber 500. As illustrated in FIG.5A, wafer 502 is cleaned by a top-side brush 504 and a bottom-side brush506 as it moves through the scrubber (from left to right). Edge rollers510 are provided to rotate wafer 502 in a counter-clockwise direction asindicated. Motors 512 are coupled to edge rollers 510 to providerotational movement to the wafer. A rotating belt edge cleaningapparatus 600 is provided along side wafer 502. As wafer 502 movesthrough scrubber 500, edge cleaning apparatus 600 is rotated upward suchthat belt 606 is pressed against wafer edge 503. Hence, as wafer 502moves through the double sided scrubber system, top-side and bottom-sidebrushes 504 and 506 clean the top and bottom surfaces of wafer 502,while rotating belt 606 removes contaminates along the edge and bevelareas of the wafer. A motor 602 is coupled to stationary roller 604 toprovide rotational movement to the edge cleaning belt 601.

One benefit of the present invention lies in the combined use oftop-side and bottom-side brushes 504 and 506 and edge cleaning apparatus600 to clean all of the exposed areas of the wafer which may becontaminated with slurry particles. This includes the top surface,bottom surface and the edge/bevel areas of the wafer. Another benefit ofthe present invention is that the rotating edge cleaning apparatus 600may be integrated into current double-side scrubber mechanism withminimal design changes to the scrubber system. In addition, since therotation of the edge cleaning apparatus is independent of the waferrotation, the relative velocity of the edge cleaning apparatus may bevaried without affecting the cleaning of the top-side and bottom-sidesurfaces of the wafer.

To further facilitate particle removal, a water jet 535 may be used topropel water into or near the point of contact between rotating belt 606and wafer edge 503, as shown in FIG. 5B. The water jet may be positionedsuch that the direction of water flows from a plane aligned with therotational axis of the wafer and contact points between the wafer andthe edge cleaning apparatus. In such a case, the water may simply carrythe particles away that are removed from the wafer by the edge cleaningapparatus or may, if at sufficient pressure, cause removal of particlesby itself. Note that the water jet is held in place by a supportstructure which is well-known in the art. In one embodiment, the waterjet is held in place above the wafer. Such a jet may be as simple as abarbed coupling with reducing barb to increase the velocity of thecreated stream. In one embodiment, the barbed coupling is ⅛″ to{fraction (1/16)}″ in diameter. In another embodiment, the jet mayinclude a nozzle that produces a fanned, knife edge pattern. Water jetsare well-known in the art. Note also that jets that spray otherchemicals may be used, instead of water, to facilitate particle removal.

Rotating belt 606 may be cleaned occasionally to remove build-up ofparticles. In one embodiment, the scrubber may flow DI water or acombination of DI water and a chemical such as NH₄OH or NH₄OH/H₂O₂mixture through itself. In an alternate embodiment, the edge cleaningapparatus may be cleaned by spraying DI or a combination of DI and achemical such as NH₄OH or NH₄OH/H₂O₂ onto belt 606 during wafer cleaningto reduce particle buildup.

In one embodiment, a splash shield (not shown) may be provided aroundthe rotating belt edge cleaning apparatus 600 to minimize the dispersionof water, chemicals and contaminates from the surface of belt 606 toother areas of the scrubber system.

Another benefit of the present invention lies in the ability to usedifferent types of materials to facilitate the cleaning of a variety ofcontaminates from the edge or bevel area of a wafer. Materials ofdifferent textures may be used within a single belt, or may beincorporated into a plurality of rotating belt edge cleaning devices. Inthis manner, one material may be used for removing one type ofcontaminate while another material may be used to remove another type ofcontaminate. FIG. 6 illustrates an embodiment of the present inventionwherein a plurality of rotating belt edge cleaning apparatus are used tosequentially clean the an edge 703 of wafer 702. As wafer 702 rotates, afirst rotating belt edge cleaning apparatus 710 containing a first belt712 of a given texture that cleans particles from edge. The edge of thewafer is then rotated toward a second rotating belt edge cleaningapparatus 714. Edge cleaning apparatus 714 includes a second belt 716that contains an outer surface having a different texture orabrasiveness than the first belt 712.

Another important feature of the present invention lies in the abilityto readily interchange belts of varying types into the edge cleaningapparatus. As a result, a standard rotating edge cleaning design may beused when cleaning any of a variety of contaminates from the edge orbevel area of a wafer. Moreover, it is important to note that materialsof different textures may be attached to the outer surface of the edgecleaning belt to enhance the belt's particle removal capability.

Thus, a method and apparatus for cleaning edges of substrates, such aswafers, is disclosed.

We claim:
 1. A method for cleaning an edge of a wafer comprising:rotating an abrasive belt along a first and a second roller having afirst and a second axis of rotation, respectively, said second axis ofrotation being fixed in relationship to said first axis of rotation;rotating the wafer about a third axis of rotation, said third axis ofrotation being not parallel to either of said first or said second axesof rotation; positioning said abrasive belt against the edge of thewafer; and controlling a force applied to the wafer with one or moresprings.
 2. The method of claim 1 wherein positioning said abrasive beltagainst the edge of the wafer comprises pivoting said first roller aboutsaid second roller to engage said abrasive belt with the edge.
 3. Themethod of claim 1, further comprising delivering a water jet to acontact area between said belt and said wafer edge.
 4. The method ofclaim 1, further comprising delivering a cleaning fluid to a contactarea between said belt and said wafer edge.
 5. A method for cleaning anedge of a wafer comprising: rotating an abrasive belt along a first anda second roller having a first and a second axis of rotation,respectively, said first and said second rollers being spring mounted toa carrier; rotating the wafer about a third axis of rotation, said thirdaxis of rotation being not parallel to either of said first or saidsecond axes of rotation; moving said carrier to engage said abrasivebelt with the edge of the wafer; and controlling a force applied to thewafer with said mounted springs.
 6. The method of claim 5, furthercomprising delivering a water jet to a contact area between said beltand said wafer edge.
 7. The method of claim 5, further comprisingdelivering a cleaning fluid to a contact area between said belt and saidsafer edge.